The investigation focuses on evaluating the effect of varying % of Red Mud (RM) reinforcement with Ordinary Portland Slag Cement (OPSC). Characterisation is done by adding 10%, 20%, 30%, 40% and 50% of RM by weight to OPSC. RM + OPSC composite mortars are made in an 8.5 × 5 × 4 cm 3 cast iron mould with external vibration keeping water-binder ratio 0.4 by weight. The mortars are cured in water for 28 days and their physio-chemical characteristics are investigated. Mortar performances like compressive strength, hardness, XRD, FTIR, SEM are diagnosed. The composite mortars cementing properties are compared with original OPSC. The result reveals the augmentation of RM with OPSC increases the hydration capacity of OPSC with improved compressive strength. The experimental optimization shows a maximum value up to 10% - 20% OPSC can be replaced by RM as filling material.
For last several years it is observed that ground granulated blast furnace slag has been widely used as a partial replacement for Ordinary Portland Cement (OPC) for concrete manufacturing. Slag as partial replacement in OPC in term uses the waste produced in steel industry, and hence reduces the carbon dioxide emissions produced during cement making [
But it is worthy to discuss that ordinary Portland blast furnace slag cement (OPSC) is a mixture of ordinary Portland cement and not more than 65 weight % of granulated slag. It is generally seen that the hardening rate of slag cement is somewhat lower than OPC for the first 28 days curing, but then increases and after 12 months the compressive strength merges with OPC. As blast furnace slag is hydraulically weak, it has glassy structure and high alkaline medium is required to neutralize the silicate-aluminate network [
The outline for red mud reinforcement in OPC or OPSC is not revealed till. The red mud is generated as a by- product (waste) material in alumina production during bauxite purification by Bayer’s process. A comprehensive outline of red mud applications is available [
At incipient red mud was collected as wet powder form from NALCO, Damonjodi, India. The as received power was dried under sunlight for 10 days to get moisture content up to 2% by weight. The red mud powder was ball milled to a specific particle size below 50 mm diameter. The composition of red mud used can be collected from [
The red mud and cement mixture was prepared separately by varying the weight % of red mud as 10, 20, 30, 40 and 50. Each mixture was thoroughly blended using an in house V-shaped blender, in order to get a uniform composite powder. Thereafter each composite powder was stirred with distilled water using a mixture (Guangzhou Xuzhong Machinery Company Limited). The water-binder ratio is maintained at a value of 0.4. The paste is poured into the cast iron mould to fill the entire volume. Casting was done by using a cast iron mould of size 8.5 × 5 × 4 cm3. Captured image of the die used for casting is shown in
using external vibrator to achieve ultimate compaction of the paste. The die was removed immediately and composite bricks are allowed to harden for 2 days and then went for curing in normal water for 28 days at atmospheric condition.
Compressive strength is the most vital property to characterise the cement. The mortars were cut to cylindrical pieces having height to diameter ratio of 5.6. The specimen was compressed between the planets of the compression testing machine (Instron-1195) by application of load as per ASTM C39 standard. The results are shown in
The results reveal an improved compressive strength up to 20% red mud reinforcement, might be due to improved hydration and structural properties approximating minimum air voids prevailing in the 20% RM composite.
Hardness of the sample was determined using Vickers hardness test equipment (LHV-1000B), applying 50 gram load with 10 seconds indentation time. The results are reported in
The IR characteristics of OPSC after 28 days hydration are identified and reported in
Wave band, cm−1 | Assigned group |
---|---|
3406.92 | (-O-H) stretch, H bonded |
1448.56 | Carbonate CO-stretch |
964.49 | Silicate SiO stretch |
860.55 | Carbonate CO bend |
537.41 | C-Br stretch |
Wave band, cm−1 | Assigned group |
---|---|
2923.76 | Bound water (H-OH stretch) |
2853.32 | Bound water (H-OH stretch) |
1743.23 | CO2 CO stretch |
1711.42 | Bound water HOH bend |
1654.00 | Bound water HOH bend |
1456.66 | Carbonate CO stretch |
952.51 | Silicate SiO stretch |
873.96 | Sulphate SO stretch |
551.70 | C-Br stretch |
541.78 | C-Br stretch |
1711.42 cm−1 band. This might be due to higher rate of hydration with RM reinforcement. As the process of hydration is the progressive conversion of free (liquid) water in capillary pores in to bound water during the cement hydration. So it is a good approximation that inclusion of RM (up to 20%) to OPSC minimizes the free water and increases bulk liquid water and structural (chemically bound) water. The C-S-H gel phase is responsible to carry significant amount of free and adsorbed water in its gel pores, and holds more tightly bound water within its inter particle spaces catalysed by RM.
Morphology of composite mortars after 28 days hydration is captured using a SEM (Scanning Electron Microscope, JEOL; JSM-6480 LV). Microstructures are shown in
The combined use of XRD, FTIR and Scanning electron microscopy techniques reveals the output results for reinforcing red mud in OPSC. It permits to study the hydration of OPSC with red mud, evaluating the variation of hydration rate and formation of phases if any. It is concluded that red mud inclusion in OPSC improves the hydration rate and increases the concrete strength. No chemical changes involve during hydration of the composite mortars as no new phases are identified. The IR technique innovates more bound water existence during hydration with red mud, attributing to H-OH stretching. Thus red mud may be used for partial replacement of OPSC up to 20% by weight and can be implemented as filling material, substituting OPSC.
All authors declare that no conflict of interest exists for publishing this research paper.
Harekrushna Sutar,Rabiranjan Murmu,Debashis Roy,Subash Chandra Mishra,Asmita Mishra, (2016) Effect of Red Mud (RM) Reinforcement on Physio-Chemical Characteristics of Ordinary Portland Slag Cement (OPSC) Mortar. Advances in Materials Physics and Chemistry,06,231-238. doi: 10.4236/ampc.2016.68023